Phagocytes are a major component of the first line of defense against infection. Our preliminary observations have suggested the existence of functionally distinct subpopulations of human polymorphonuclear leukocytes (PMN's). This study has been designed to verify those observations and to extend them. We will evaluate several techniques for the physical separation of PMN subpopulations including: adherence to glass, plastic or nylon wool; centrifugation on albumin density gradients; taking advantage of Fc receptors and C3b receptors; migration in electric fields; and elutriation. We will analyze the subpopulations obtained by a variety of functional tests: bactericidal activity against a battery of microbes, chemotaxis, content of selected microbicidal enzyme systems (H2O2 generation, superoxide generation, myeloperoxidase), alkaline phosphatase, antibody-dependent (ADCC) and mitogen-induced cellular cytotoxicity (MICC), presence of Fc and C3b receptors, chemotaxis, activation by lymphokines, lectin binding and direct binding of bacteria. When methodology has been established to consistently analyze PMN subpopulations selected patients (i.e., burned or traumatized) will be studied to determine if the PMN dysfunction we have previously described in such patients is due to shifts in PMN subpopulations.